Known types of steering locks usually make use of a retractable lock bolt for the purpose of preventing any rotation of the shaft of the steering column. This bolt is carried by a structural element of the vehicle, and when the steering lock is engaged, the bolt is deployed into a recess formed in the shaft of the steering column, so as to prevent the latter being turned about its axis.
Such a device, in spite of the fact that it is so widely used, has a certain number of disadvantages. First, when the driver of the vehicle activates the locking system, locking does not take place automatically. In this connection, the steering lock is not properly effective, unless the bolt is engaged in the recess, which is only possible if the recess, and therefore the steering column, occupies a particular rotational position in which it is aligned with the bolt. While it has been proposed to provide the steering column with a set of several recesses, spaced apart angularly at regular intervals around the steering column shaft, on most occasions, the driver still has to maneuver the steering wheel before the steering lock can be properly engaged, so as to put a recess in the steering column into register with the bolt and thereby lock the antitheft device effectively.
This effective operation is generally detectable by a click which occurs as the bolt of the steering lock comes into its locked position. The steering column and the steering wheel then have no more than a very limited angular displacement.
In addition, such a conventional design of a steering column lock obliges the driver to act on the steering wheel at the instant of unlocking, so as to enable the bolt to be disengaged from the recess in the steering column shaft. In this connection, the friction forces of the bolt against the side walls of the recess can prevent withdrawal of the bolt, and it is necessary to effect an angular displacement of the bolt in the recess in order to be able to release the bolt, by eliminating the contact with the walls of the recess.
In addition, in current practice, during an attempt by a thief to break the steering lock, a very high torque is applied to the steering column through the steering wheel, in order to break the bolt or one of its actuating elements.
If the bolt and its actuating mechanism resist such efforts, the thief will try and apply even more force to the steering column, which can lead to damage to other parts of the steering system, such as the steering wheel or even the support of the steering column shaft.
On the other hand, if the bolt and its mechanism do yield, it can become possible to drive the vehicle. However, rupture of one of the components of the mechanism can give rise to serious problems as to operational reliability. The steering column may then become jammed while the vehicle is in motion.